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PLASMA DEPOSITED THERMOCOUPLE FOR NON INVASIVE TEMPERATURE

MEASUREMENT

SHAHINA P.AS8 EIROLL NO:61

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CONTENTSINTRODUCTIONTEMPERATURE MEASUREMENTLYOPHILIZATION PROCESSPRINCIPLE OF FREEZE DRYINGPROBLEMS OF FREEZE DRYINGPROPOSED SYSTEMPLASMA SPUTTERED TCREALIZATIONCONCLUSION

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INTRODUCTIONDescribes the realization of temperature

sensor Based on plasma sputtered thermocoupleRealized in vacuum with quite pure materialsNegligible oxidationAccurate measurement Made inertThickness of few nanometersApplication in lyophilization process

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TEMPERATURE MEASUREMENTTemperature is local parameterThermocouples for temperature

measurementCan be less invasiveConsumes negligible powerRealize in flexible and cylindric probes

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With these advantages, but thermocoupleAlter temperature distributionMetalic materials react with surrounding

environmentThese 2 problems occur in preeze drying of

lyophilization process

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LYOPHILIZATION PROCESSProcess of drying a substance by sublimationPreliminary frozen at -20⁰cPressure reduced to few pascalsSo sublimates slowlyLeaving dried powderMost pharmaceutical powders are made by

this method

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Principle of freeze dryingDrying by sublimationFrozen liquid to gaseous stateTransfer of ice to water vapour Function of pressure and ice temperatureExpensiveRequires specialized equipment

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Freeze drying consists of 3 stages Freezing Primary drying Secondary dryingDuring freezing solution- solidDuring 1⁰ drying ice removed by sublimation2⁰ drying is for isothermal desorption

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Advantages of freeze drying• Do not need refrigeration• Can be stored at ambient temperatures• Can be completely reconstituted with water• Stable over 2 year life

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GRAPHICAL REPRESENTATION OF FREEZE DRYING

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PROBLEM OF FREEZE DRYINGWhen pressure reduced, drying begins Product tyemperature decreasesSublimation is endothermicMost of energy is by radiationie, quite low at low temperature tooLead to temperature of product go down -50⁰

c to -70 ⁰cTurns long lyophylization times

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Possible solution isTo model drying processSupply heatBut this lead to another problemThermal conductivity between shelf and

product is higherie ,sublimatiom is slower

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A good and easy solution is thatTo monitor the temperature inside the

product in several points within the chamberBut it will alter drying proceessAnd intoxicate the materialSo possible solution is…..To measure temperature near to productNot in contactEg: on external wall of vial

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PROPOSED SYSTEM

Fig. 1. Two thermocouples deposited on the external part of a vial tocheck the deposition effectiveness on curved surfaces. The vial shows twocopper/copper-nickel thermocouples both with a junction at the top of the vial, but with the other junction at different heights. In the picture also the wires used to collect the thermocouple voltage

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Extremely thin and sealed TCDeposited via plasma sputteringFor local measurement- thin TCLow response timeSealed devices for specific applicationsPresent proposal uses a protective Siox thin

film

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Thickness of few tens of nmTo avoid contact between metal and drying

substanceThis way TC can deposited on vial internal

surfaceAble to follow temperature changes

accuratelyWithout altering the lyophilized material

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PLASMA SPUTTERED THERMOCOUPLEA TC can be made by 2 different materialsTo form 2 junctionTo measure voltageProportional to temperature difference Materials are… iron, copper, constantan, chromel, alumel,

platinum, rhodium; each couple having specific electrical and chemical properties.

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Several metal couples for drying processChoice related toThermoelectric powerEasiness of plasma depositionChemistry of TC/Siox interfaceIn order to ensure good adhesion

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• To optimize plasma process few considerations are

Plasma pretreatment to improve adhesion To reduce no: of defects of deposited coatingTo improve barrier properties Plasma pretreatment carried out in noble as

well as reactive gasesSuch as oxygen and hydrogen

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• According to metal Iron –pretreatment in oxygen plasmaAluminum- metal surface reduction by

hydrogen glow dischargeAll these require 2 step depositionBut Cu and Ni not require surface

modificationSo all specimens made of T type TC(Cu/CuNi)Thermoelectric power -50 μV/◦C

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Thickness of active materialsThin layer allows non invasive sensorsBut high electrical resistanceThick layer alows more invasiveProduces low resistance, but large sputtering

timesSo here proposed range 50nm to 500nm

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REALIZATIONTo realize Cu/CuNi strips the active materials

deposited on glass substrateGlass substrate is for good adhesionDepositions done at room temperature 100 w of input power by argon as discharge gasDeposition rate forCu and constantan .1nm/s

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Siox protective layer to coat thermocoupleWithout exposing samples to air and

environmental contaminations2 step deposition is required for deposit Siox

loyerThe SiOx film can be deposited by using aplasma which is fed with constant

tetraethoxysilane (TEOS),oxygen and argon flow rate of 1, 20 and 20 sccm respectively, at 5 Pa of pressure and 100 W of input power.

The thickness in this case was selected to about 200 nm.

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Fig. 4. The first prototype of inert thermocouple (ITC). The picture showsthree strips which are sputtered on a flat glass to form two thermocouples.The TCs are covered by a 185 nm layer of SiOx which is the responsiblefor the translucent aspect

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Fig. 7. A FESEM image of the cross section of the constantan/SiOxinterface. The constantan thickness is of about 150 nm, while the SiOx layer has a thickness of about 185 nm. The SiOx protecting layer appears quite compact so that a quite good protection should be expected.

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CONCLUSIONAn innovative way to create non invasive

temperature sensor Temperature mapping can be obtainedAccurate measurement

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REFERENCESIEEEwikipedia

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